Imran Khan, the cricketer-turned-politician, is launching his own emergency fundraising appeal for the victims of the devastating floods in Pakistan, pitting him directly against the government's own efforts.

The Imran Khan Flood Relief organisation will seek to tackle both the immediate emergency and the long-term rehabilitation work required. "The government has totally collapsed, there's no government here," Khan told the Guardian. "The government's efforts to raise money have totally failed because no one trusts the government."

Khan will seek to mobilise thousands of Pakistanis behind his cause, to produce an army of volunteers to carry out the work. The floods have ravaged at least a fifth of the land mass of Pakistan and has hit 20 million people, with the waters continuing to envelop new areas.

The required funding to deal with the calamity has not been forthcoming, either domestically or internationally, and there has been bitter criticism of the Pakistani president, Asif Ali Zardari, for not visiting the flooded areas for several days.

Yesterday the UN appealed again for money, saying it was desperately short, having raised $160m (£100m) of the $460m required to cover just the first 90 days of the disaster. The World Bank announced it would make $900m immediately available for the crisis.

Pakistan's prime minister set up an emergency relief fund two weeks ago for Pakistanis to give to, but as of Monday it had only managed to attract 117m rupees (£900,000). It is estimated that billions of pounds will be required to deal with the damage to infrastructure, housing and agriculture.

"The money coming into Pakistan is peanuts, so I decided I had to do something," said Khan. He is seeking contributions from Pakistanis at home and abroad, and will run telethons on Pakistani TV, as well as leading a caravan roadshow across the nation to garner support.

He said his charity would work with other non-governmental organisations.

Khan has an established record as a philanthropist, having started a cancer hospital and a college in Pakistan, which he still runs. He raises about $20m a year to maintain the hospital, which gives free treatment to three-quarters of its patients.

Though his politics attract much criticism, he is widely seen in Pakistan as free of corruption, which his fundraising campaign for the floods will now bank on.

By contrast, Zardari has faced graft allegations in the past and stories surface daily in the Pakistani press about government corruption. Pakistan comes close to the top of international league tables for corruption, one of the reasons suggested by some for the reluctance of individuals and countries to contribute to the emergency.

The Pakistan government says it is doing all that is possible for the flood victims, given the scale of the disaster and the resources it has available.

"The task cannot be handled by the government alone or by any political party or institution. It can be met only through the combined effort of the whole nation," Zardari said today.

Khan heads his own political party, Pakistan Tehreek-e-Insaf. Although it has yet to make any significant inroads in elections, his work for the flood victims could become controversial and be seen as political.

He is an unrelenting critic of Zardari and of US foreign policy. According to his critics, he is allied with the Islamic right.

The international community has pledged $353m to the floods cause, though much of that money has yet to be delivered. The US heads the list of donors with $76m, followed by the UK, which has earmarked £31.3m. Earlier this week, Nick Clegg called the international response "pitiful".

Although there has been criticism of Muslim countries not giving enough, Saudi Arabia has delivered $44m, while Turkey is to give $11m.